In also the world of digital circuits, trends of speeding up operations proceed, so that there were the cases wherein, for example, operation characteristics of a semiconductor chip to be mounted are affected by a finished state of a board circuit as in the world of analog circuits. Characteristic impedance of line (wiring) is decided by a type of materials, a distance of an insulating material to be inserted between the board and a plate-like ground layer, or a pitch defined between leads and the like. In this respect, since such board circuit is fabricated in a dimension region which is close to the limit of the present manufacturing engineering, it can be made clear for the first time whether or not the resulting board circuit is the one which is suited for operation characteristics of a semiconductor chip to be mounted after having been finished. In the world of analog circuits, matching work is conducted to readjust a joined position of parts while confirming operation characteristics of a semiconductor chip, whereby adjustment has been performed.
At present, since use of a wiring board such as a TAB (Tape Automated Bonding) tape becomes possible, fine wiring with 30 micron (μm) to 60 μm pitch can be made.
As a result of studying the above described prior art, the present inventors have found the following problems.
There is such a problem that since the number of products to be fabricated increases extraordinarily in the world of the above described conventional digital circuits, it becomes very difficult to apply matching work in a manner of individual response.
With respect to a systematic malfunction, merely such a manner that a typical sample is selected to make clear a procedure for adjusting operation, and a manner for such adjustment is incorporated in a flow of working processes may be adopted. Accordingly, there is such a problem that a manner of adjustment which can be incorporated in such an assembly-line method must be at least ensured.
On one hand, speeding up of data transmission brings about a new problem in generation of noise due to electromagnetic field coupling appeared between leads of fine pitch wiring in a wiring board such as the above described TAB tape, and such problem became the one which cannot be disregarded. There was such a problem that a ringing (resonance) phenomenon arose between leads which are disposed apart from one another with 30 μm interval, so that a signal waveform of clock pulse gets remarkably out of shape.
For instance, when a BGA (Ball Grid Array) of CSP type is mounted as a semiconductor device, influence of noise due to a mutual inductance between wiring leads in a package becomes a problem in view of operation characteristics.